I. Field of the Invention
The present disclosure relates generally to the fields of chemistry and materials science. More particularly, it concerns metal-organic frameworks, compositions thereof and methods use thereof, including for separating gas molecules, sensing, heterogeneous catalysis, drug delivery, lithium sulfide battery, membrane and analytical devices.
II. Description of Related Art
Microporous metal-organic frameworks (MOFs) have emerged as a new type of porous materials for gas storage, separation, sensing and heterogeneous catalysis. The tunable pores and the immobilized functional sites within such microporous MOFs have enabled them to direct specific recognition of certain molecules based upon size and functionality.
Control of pore sizes and pore surfaces within porous materials is useful for their ability to selective recognize and thus separation of small molecules, and the pores within such porous MOFs can be systematically modified simply by the change the secondary building blocks (SBUs), changing the organic bridging linkers, or the control of the framework interpenetration (Deng et al., 2010; Chen et al., 2010; Ma et al., 2010; Horike et al., 2009). To tune the micropores to induce their size specific encapsulation of small gas molecules, various series of microporous metal-organic framework materials have emerged as promising microporous media for the recognition and separation of small gas molecules (Kitaura et al., 2004; Chen et al., 2004; Cho et al., 2006; Liu et al., 2010; Murray et al., 2010; Ma et al., 2009; McKinlay et al., 2008; Dubbeldam et al., 2008; Chen et al., 2006; Finsy et al., 2008; Bae et al., 2010; Zhang et al., 2008; Dybtsev et al., 2004; Li et al., 2009; Vaidhyanathan et al., 2006; Nuzhdin et al., 2007; Dybtsev et al., 2006; Chen et al., 2008).
The discovery of new energy resources, particularly natural gas in the form of shale gas in the United States, is facilitating the implementation of natural gas as a viable alternative energy source. The United States has the commercialization capability to produce large-scale shale gas at a cheaper cost than other countries, which makes natural gas appealing as a new fuel (Armor, 2013). In order to accelerate such a fuel switching from coal/petroleum to natural gas, suitable materials for natural gas storage and transportation need to be developed. While Compressed Natural Gas (CNG), stored as supercritical fluid at room temperature and 200-300 bar in steel cylinder, might be still suitable for large vehicles such as trucks, Adsorbed Natural Gas (ANG) is better suited for daily use cars for both the cost and safety reasons.
Among the diverse porous adsorbents for methane storage (methane is the main component in natural gas), porous metal-organic frameworks (MOFs) are promising for such a purpose because of their high porosities, tunable pores and easily immobilized functional sites to optimize their storage capacities (O'Keeffe et al., 2012; Horike et al., 2009; Férey and Serre, 2009; Zhang et al., 2012; Yan et al., 2013; Wang et al., 2013; Sumida et al., 2012; Getman et al., 2012; Wu et al., 2012; Wilmer et al., 2013; Wu et al., 2009; Park and Suh, 2013 and Jiang and Xu, 2011). BASF has commercialized some prototypic MOFs as well as demonstrated model vehicles fueled with natural gas by making use of BASF MOF materials (BASF MOF Materials for Energy Storage). In order to fully implement natural gas fuel systems for vehicles, target adsorbents with high methane storage capacities need to be developed. The Advanced Research Projects Agency-Energy (ARPA-E) of the U.S. Department of Energy (DOE) developed methane storage targets to guide the research on adsorbent based methane storage with the goal of a volumetric storage capacity of 350 cm3 (STP) cm−3 for the adsorbent material at room temperature (DOE MOVE Guidelines). Without the consideration of packing loss, according to the guidelines, the volumetric storage capacity needs to be higher than 263 cm3 (STP) cm−3, equivalent to that of CNG at 250 bar and 298 K. Furthermore, the DOE set a target of the gravimetric energy density of 0.5 g (CH4) g−1 (adsorbent) for new adsorbent based methane storage materials.
Although the potential of MOF materials for methane storage has been conceptually established, reaching the DOE targets in practice has been challenging. Since the discovery of the first MOFs for methane storage, (Kondo et al., 1997 and Eddaoudi et al., 2002) significant progress has been made to improve the methane storage capacities of MOF materials over the past decade; however, their storage capacities are still far away from the DOE target (He et al., 2012 and Makal et al., 2012). Recently, three independent groups realized a unique MOF, HKUST-1 (Chui et al., 1999), for high methane storage with volumetric storage capacity of 259-267 cm3 (STP) cm−3 at 65 bar and room temperature (Peng et al., 2013 and Mason et al., 2014). This was the first MOF material whose volumetric methane storage capacity to reach the DOE target if packing loss is not considered.
The saturated gravimetric methane storage capacities of MOF materials are basically determined by their porosities (pore volumes and/or BET surface areas) (Peng et al., 2013; He et al., 2013; Kong et al., 2013 and Feldblyum et al., 2013). In order to optimize volumetric methane storage capacities, MOFs balance porosities and framework densities with a high densities of functional sites/groups and pore cages for the recognition of methane molecules (He et al., 2013; Gedrich et al., 2010; Ma et al., 2008 and Guo et al., 2011). The MOF-505 series of MOFs of NbO type structures meet these criteria and are of interest (Chen et al., 2005 and Lin et al., 2006).